Virtual machine storage migration

https://github.com/migtools/mig-controller/pull/1389/files#virtual-machine-storage-migrationMigration toolkit for containers now supports storage migration for KubeVirt virtual machines. Migration can happen offline (virtual machine is turned off) as well as online (virtual machine is running).

Main use cases for this functionality is migrating from one storage class to another. For instance if one is rebalancing across different storage providers, or some new storage is available that is better suited for the workload running inside the VM.